drm/i915/skl: Read out crtl1 for eDP/DPLL0

v2: Put the DPLL0 state readout in skylake_get_ddi_pll(), closer to
where the PLL assignement read out is done rather than the frequency
readout function. (Daniel)

v3: Remove stray new line (Damien)
    Add Paulo's r-b tag for v1

Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com> (v1)
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>